In the technical field of the mobile communication systems, research and development for the next-generation communication systems have been rapidly accelerated. According to a communication system currently being considered, a single carrier system has been proposed to be used as uplink communication in the viewpoint of extending the coverage area while controlling the Peak-to-Average Power Ratio. Further, in the communication system using the single carrier method in the uplink communications, radio resources are appropriately allocated in both uplink and downlink in the form of a shared channel (SCH) in accordance with the communications status of the users. This process of determining of the allocation the radio resources is called scheduling. To appropriately perform the uplink scheduling, each user equipment transmits the pilot channel to the base station and the base station evaluates the uplink channel quality by checking the receiving quality of the pilot channel. Further, to perform a downlink scheduling, the base station transmits the pilot channel to the user equipment and the user equipment reports the CQI (Channel Quality Indicator) indicating the channel status based on the receiving quality of the pilot channel. Based on the received CQI from each equipment, the base station evaluates the downlink channel quality and performs the downlink scheduling.
As the data of an uplink control channel, there are control information items (hereinafter may be referred to as “essential control information items”, “first control information”, or “first control channel”) that should be transmitted along with the data of an uplink data channel and other control information items (hereinafter may be referred to as “second control information” or “second control channel”) that are transmitted regardless of the presence of the uplink data channel. The first control information may include information items necessary for demodulating the data channel such as the modulation method of the data channel and the channel coding rate. The second control information may include information items such as the downlink channel CQI, the downlink data arrival acknowledgement information (ACK/NACK), and a resource allocation request. Therefore, there are cases where the user equipment transmits only the first control information, only the second control information, or both first and second control information via the uplink control channel.
When a resource block (radio resource) is allocated for the uplink data transmission, the first control information (and, on an as needed basis, the second control information) are transmitted via the allocated resource blocks. However, in a case where the uplink data channel is not being transmitted, it is under consideration that the second control information is to be transmitted via a dedicated resource (dedicated frequency bandwidth). In the following, examples where a frequency bandwidth is used in such a way are briefly described.
FIG. 1 shows an example how uplink frequency bandwidths are being used. In the example of FIG. 1, there are provided two different data sizes of resource units (hereinafter may be simplified as resources) having a larger size and a smaller size, respectively. In FIG. 1, the larger resource unit has a frequency bandwidth (FRB1) of 1.25 MHz and a duration time (TRB) of 0.5 ms and the smaller resource unit has a frequency bandwidth (FRB2) of 375 kHz and a duration time (TRB) of 0.5 ms. The duration time corresponds to a period of a single radio packet data and may be referred to as a unit transmission period, a TTI (Transmission Time Interval), a sub-frame and the like. There are six (6) resources provided along the frequency axis and the size of the left end resource and the right end resource is smaller in the frequency domain than other four (4) resources. However, the pattern of the resource allocation may be determined in various ways and what is only required is that the determined pattern should be known to both the transmitting side and the receiving side in advance. In the example of FIG. 1, the uplink scheduling is performed so that the control channel (first control channel) to be transmitted along with the data channel and, on an as needed basis, the second control channel are to be transmitted using a part of the periods of larger resources (whose resource numbers are 2 through 5). Further, the transmission timings of the user equipment is adjusted so that the control channel (second control channel) is to be transmitted using the smaller resources (whose resource numbers are 1 and 6) while no uplink data channel is transmitted. Further, it is arranged so that the second control channel of certain user equipment is to be transmitted using two smaller resources. In the example of FIG. 1, the second control channel of user equipment “A” is to be transmitted using the 6th resource in the 2nd subframe and the 1st resource in the 3rd subframe. Similarly, the second control channel of user equipment “B” is to be transmitted using the 6th resource in the 3rd subframe and the 1st resource in the 4th subframe. As described above, the second control channels are transmitted by hopping in the time and frequency axis directions, therefore, it may become possible to obtain time and frequency diversity effects, thereby increasing the reliability of the appropriate demodulation of the second control channel in the base station.
FIG. 2 shows another example how uplink frequency bandwidths are being used. Similar to the case of FIG. 1, there are also provided two different data sizes of resources having a larger size and a smaller size, respectively. In this example, however, with respect to the smaller resources (1st and 6th resources), the period TRB of the subframe is further divided into two sub-time periods. In the example of FIG. 2, the second control channel of certain user equipment “A” is to be transmitted using a first sub-time period of the 1st subframe (a first half period of the subframe) of the 1st resource and a second sub-time period of the same 1st subframe (a second half period of the same subframe) of the 6th resource. Similarly, the second control channel of user equipment “B” is to be transmitted using a first sub-time period of the 1st subframe of the 6th resource and a second sub-time period of the same 1st subframe of the 1st resource. The transmission of the second control channels of the user equipment “A” and “B” in the 1st subframe is similarly repeated in 3rd and 5th subframes. As described above, the second control channels are transmitted by hopping in the time and frequency axis directions, therefore, it may become possible to obtain time and frequency diversity effects, thereby increasing the reliability of the appropriate demodulation of the second control channel in the base station. Further, in this example of FIG. 2, the transmission of the second control channels of both user equipment “A” and “B” is completed within the 1st subframe. Therefore, this example of FIG. 2 is preferable in the viewpoint of reduction of transmission delay in the uplink control channel. This technique is described in, for example, Non Patent Document 1.
Non Patent Document 1: 3GPP, R1-061675
Non Patent Document 2: 3GPP, R1-060099
Non Patent Document 3: 3GPP, R1-063319